Opposing seasonal dynamics in phylogenetic and flower color diversity of co-flowering wildflower assemblages

Flower color is a key trait mediating plant-pollinator interactions, yet the ecological rules governing its distribution across co-flowering assemblages remain poorly understood. We examined spatiotemporal patterns of flower color and phylogenetic diversity in Eastern North American wildflowers to test for non-random community structure, seasonal shifts, and associations between flower color similarity and phylogenetic relatedness. Using occurrence, phenology, and color data from community science datasets, we reconstructed communities of co-flowering assemblages and calculated standardized effect sizes of mean pairwise distances for both flower color and phylogenetic relatedness. We analyzed seasonal trends using mixed models and assessed whether closely related species co-flowered non-randomly with respect to color similarity using bootstrap correlations. We found that, on average, co-flowering assemblages were overdispersed for both flower color and phylogeny. However, flower color dispersion significantly decreased over the growing season, while phylogenetic dispersion significantly increased, reflecting a pattern in which co-flowering assemblages shifted to more distantly related but similarly colored assemblages. Finally, color and phylogenetic dispersion were negatively correlated across communities, indicating that communities composed of more closely related species tended to exhibit more dissimilar flowers. Together, our results suggest that wildflower assemblages in Eastern North America show detectable, non-random structure across space and time with respect to color and relatedness at the broad scale, and that mechanisms underlying the structure of co-flowering groups may shift throughout the growing season.